In DE-A 3 702 999, an apparatus for irradiating fluids is disclosed which includes a transparent conduit through which fluid flows and which is irradiated by a radiation source. In this case, the fluid is a UV-hardening reaction resin, which flows through a tube which is irradiated by a UV radiation source, and is then applied to the treatment area, where the resin is activated by the irradiation and subsequently polymerizes.
The intensity of the radiation and thus the rate of activation decreases exponentionally with the thickness of the irradiated fluid layer. The known device therefore works with a relatively thin tube, and a reflector is positioned on the side of the tube opposite the radiation source, such that the fluid flowing through the tube is irradiated from two opposite sides. In one variation the radiation is conveyed through a cylindrical rod, and the fluid to be irradiated flows coaxially along the rod. In a further variation the known device is configured such that a thin flow layer is formed along a flat or slightly curved, irradiated surface.
The problem of irradiating thin flowing layers uniformly with electromagnetic radiation also occurs in the sterilization of fluids. FR-A-25 00 948 discloses a device for this purpose, in which centrifugal forces cause a thin layer of the fluid to climb up the inner wall of the rotating tapered vessel, where it is irradiated by fluorescent tubes projecting into the vessel.
The known devices present the difficulty that, in order to achieve homogeneous irradiation of the entire fluid, a layer must be formed which is as thin as possible; furthermore, because the flow rate is limited by the amount of energy per unit volume required for activation, polymerization or sterilization as the case may be, the surface of the thin fluid must be made correspondingly large to achieve a volume flow rate usable for practical purposes; but the larger the surface area, the more difficult it is to irradiate it homogeneously with available light sources.
The preactivation of polymerizable fluids, such as adhesives, presents the further difficulty that polymerization begins after activation. As a result, an ever thicker layer of fluid grows on the wall of the vessel through which the fluid flows, on which the flow rate is zero, which not only increasingly diminishes the cross-section of the flow, but also absorbs an ever-increasing percentage of the radiation.
The patent of addition FR-90710 discloses a device in which a fluid of addition is conveyed through tubes, which are positioned opposite a flat ionizating radiation source. Rigid rods are located in the tubes and carry spiral ridges on their outer surfaces, in order to ensure that those parts of the product which enter the tube on the side turned away from the radiation source are also exposed to radiation.
GB-A-639 467 discloses yet another arrangement, in which the product flows through a tube furnished with a spiral groove on its inner wall. Again, the groove ensures that all parts of the product are brought at least once to a position facing a radiation lamp lying parallel to the tube.